measure DC current switching current

i am seeking an accurate means to measure the current value on reversing DC circuitry in milliseconds. that is 6seconds forward on and 0.8seconds reverse polarity at 1/10th of the voltage of forward... this is in refference to an ECM application where the reverse expells the potential buildup for the Titanium electrode apx 0.050" diamater with a resultant oriface of apx 0.060" +/-0.050